Ricin and Shiga toxin belong to a group of protein toxins with targets in the cytosol. These toxins consist of one moiety that binds the toxin molecule to cell surface receptors, and another enzymatically active moiety that enters the cytosol after endocytic uptake of the toxin. The toxins are of current interest in relation to disease and the construction of immunotoxins. Moreover, they have proven useful to investigate mechanisms of endocytosis and to follow intracellular pathways of transport. Some of the recent results obtained with ricin and Shiga toxin are discussed.